This invention relates to a linear variable differential transformer for generating an electrical output signal in accordance with a sensed position related or transduced signal.
A variably positioned means, or any variable which can be converted to a related position movement, may be transduced to an electrical signal by coupling the positioned means to a linear voltage differential transformer. Generally, such a transformer includes a centrally located primary winding with a pair of secondary windings located to the opposite side of the primary. The secondary windings are connected in series opposition such that the induced voltages, resulting from energizing of the primary winding, subtract from each other and produce an output signal equal to the voltage difference. A movable iron core rod is mounted extending across the primary completely and partially across the aligned secondaries to control the coupling of the primary winding to the secondary windings. Generally, as the core rod moves from a centered position, the number of turns of the two secondary windings and the level of flux linkage with the two secondaries varies oppositely and the output voltage of the two secondary windings varies with the position of the core. With the core centered between the two secondaries, the primary flux is essentially similarly coupled to both secondary windings and the output voltages are essentially equal; producing a zero output signal. If the core is positioned to a first limit at which the primary winding is coupled essentially completely to one of the secondary windings, the primary flux is coupled to the total number of winding turns of that secondary winding, and the amount diverted through that secondary winding is increased providing a corresponding relatively large output voltage. The opposite secondary would effectively be decoupled and an insignificant output voltage would be created therein. By moving of the core to the opposite limit, a reverse voltage signal is generated.
In a practical construction, the primary coil is energized from a suitable high frequency oscillator source, while the secondary windings are connected in series to a suitable demodulator circuit to produce a resultant DC voltage signal.
The linearity of the output is dependent upon employing essentially identical secondary coils which are accurately mounted with respect to the primary to effect the similar coupling and decoupling in response to the positioning of the core. Further, the movable core rod necessarily results in a significant air gap in the structure resulting in a reluctance characteristic which minimizes the output signal. Generally, sophisticated sensing circuitry is required to provide an appropriate output signal. High nickel alloy magnetic frames have been used with the core rod extended substantially between the ends. Such structures have generally been constructed to sense a very small movement as the opposite ends of the rod move relative to the end face frame members. Further, they have used very special magnetic materials which are costly.
There is, therefore, a need for a compact and inexpensive linear differential transformer which can sense intermediate degress of movement, particularly for use as a transducer in which a variable is converted into a motion and in which the amplitude of movement can be selected.